# Gray unit (Gy)

Source: https://onco.cc/terms/gray-unit/  
OnCo record `gray-unit` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The unit of radiation dose absorbed by tissue: one gray is one joule per kilogram. A curative course is typically 50-70 Gy in total; a single bone-pain treatment is 8 Gy. Radiopharmaceuticals are prescribed by activity in becquerels (GBq) instead.

## Summary

Because biological effect depends on both total dose and dose per fraction, different schedules are compared with the equivalent dose in 2 Gy fractions (EQD2) or biologically effective dose (BED); cervical brachytherapy aims for ≥85 Gy EQD2, early lung SBRT for BED ≥100 Gy. Dose escalation beyond 60 Gy did not help in stage III lung cancer (RTOG 0617) but did in prostate cancer. For radioligand therapy the administered activity (7.4 GBq of 177Lu-PSMA-617) is fixed, and dosimetry estimates the resulting gray to tumour and kidneys. Whole-body doses above about 4 Gy are lethal without marrow rescue, which is the basis of total body irradiation conditioning.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: cGy; centigray; EQD2; BED; biologically effective dose; dose escalation; dose-escalated; radiation dose; absorbed dose; prescribed dose; total dose; 60 Gy; 70 Gy; GBq; MBq; becquerel

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Gray_(unit)
- Wikipedia: https://en.wikipedia.org/wiki/Gray_(unit)

## Connected records

- terms: [Brachytherapy (internal radiotherapy)](https://onco.cc/terms/brachytherapy-term/), [Conditioning regimen (myeloablative, reduced-intensity)](https://onco.cc/terms/conditioning-regimen/), [Dosimetry](https://onco.cc/terms/dosimetry/), [Hypofractionation (fewer, larger radiotherapy doses)](https://onco.cc/terms/hypofractionation/), [IMRT / IGRT / VMAT (modern external beam radiotherapy)](https://onco.cc/terms/imrt-term/), [Re-irradiation](https://onco.cc/terms/re-irradiation/), [Stereotactic body radiotherapy (SBRT / SABR)](https://onco.cc/terms/sbrt-term/)
- fronts: [Radiation Therapy](https://onco.cc/fronts/radiation/), [Radiopharmaceuticals & Theranostics](https://onco.cc/fronts/radiopharma/)
- technologies: [Radioligand therapy (beta emitters)](https://onco.cc/technologies/radioligand-therapy/), [The linear-quadratic model and fractionation](https://onco.cc/technologies/linear-quadratic-model/)

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